1. Field of the Invention
The present invention relates to a liquid crystal display device in which the display gray-scale of a liquid crystal panel can be adjusted, and a liquid crystal driving circuit therefor.
2. Description of the Related Art
A conventional liquid crystal driving circuit inputs display data, generates gray-scale voltages, selects the gray-scale voltage corresponding to the given display data and then outputs the gray-scale voltage thus selected to a liquid crystal panel.
For example, in a liquid crystal driving circuit for outputting 64-gray-scale voltages, 8-gray-scale voltages are generated by resistance-dividing each section between two respectively adjacent reference voltages of 9 levels supplied from an external device, and finally 64-gray-scale voltages in total are generated. The gray-scale voltage corresponding to each display data is selected from the 64-gray-scale voltages thus generated, and output to the liquid crystal panel.
For example, 1994 SID INTERNATIONAL SYMPOSIUM DIGEST of TECHNICAL PAPERS 23:2 (pp. 351-354) discloses a liquid crystal driving circuit for generating and outputting gray-scale voltages on the basis of reference voltages supplied externally.
In this liquid crystal driving circuit, a reference voltage is adjusted to generate and output a gray-scale voltage to a liquid crystal panel having a non-linear brightness vs. applied voltage characteristic as generally shown in FIG. 4 so that the output voltage to the display data is matched with the characteristic of the liquid crystal panel.
However, in the conventional technique, the resistance values of voltage-dividing resistors are fixed, and eight gray-scale voltages generated on the basis of two reference voltage values have a linear relationship. When the gray-scale voltage is near to 1V or 4V, the eight brightness values thus obtained have a non-linear relationship to the gray-scale code as shown in FIG. 4 of the prior art as in the case of transmittance.
Accordingly, it is insufficient to merely adjust the reference voltage in order to adjust the display brightness balance (gray-scale display characteristic) of each gray-scale. Therefore, it has hitherto been difficult to perform .gamma.-correction to correct distortion of the gray-scale display characteristic due to an inherent characteristic of a device, and implement a gray-scale display characteristic and a color tone which are matched with a user's taste or suitable for displaying a target image.
An object of the present invention is to provide a liquid crystal driving circuit and a liquid crystal display device which can adjust the display brightness and the variation characteristic of color to display data values input.